<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        #test {
            width: 200px;
            height: 200px;
            margin: auto;
            background-image: linear-gradient(90deg,red,orange,yellow,green,blue,indigo,violet);
        }
    </style>
</head>
<body>
    <div id="test">

    </div>
</body>
</html>
